The subject matter of the present invention is related to the subject matter set out by the same inventors (Steven E. Cornelius and Lonnie C. Goff) in a co-pending patent application Ser. No. 09/150,120, filed Sep. 9, 1998, for A HYBRID ONE TIME PAD ENCRYPTION AND DECRYPTION APPARATUS WITH METHOD FOR ENCRYPTING AND DECRYPTING DATA, assigned to the same assignee. The disclosure of the above-referenced application is incorporated by reference into this application.
The present invention concerns encryption/decryption of data and pertains particularly to the parallel connection of encryption blocks to enhance security and performance of cryptographic devices.
In order to protect against theft or misuse, secure information within a computing system can be encrypted before being stored within the computing system and/or transmitted to another computing system. Before a computing system uses encrypted information, the encrypted information is decrypted. For example, encryption and decryption is often performed in accordance with the Data Encryption Standard (DES). See for example, Data Encryption Standard (DES), Federal Information Processing Standards Publication (FIPS PUB) 46-2, Dec. 30, 1993 available from the U.S. Department of Commerce, Technology Administration, National Institute of Standards and Technology. See also DES Modes of Operation, Federal Information Processing Standards Publication (FIPS PUB) 81, Dec. 2, 1980 available from the U.S. Department of Commerce, National Bureau of Standards.
There are various techniques used to attack security systems. For example, in a brute-force ciphertext-only attacks, all possible combinations of keys can be tried in order to discover the plain text. Depending on the length of a secure key and other factors, an eavesdropper can, in some cases, successfully perform a DES brute-force ciphertext-only attack in a matter of hours.
Plaintext attacks (e.g. Differential Cryptanalysis) can be more efficient than brute-force attacks. In plaintext attacks, the correlation between plaintext and its resultant ciphertext is used in more clever ways than brute force attacks in order to discover the sender""s key. Depending on the length of a secure key and other factors, an eavesdropper can often successfully perform some form of intelligent plaintext DES attack in 3 to 15 minutes.
It is desirable, therefore, to increase the security of information in order to make the information less vulnerable to discovery by an unauthorized user.
In accordance with the preferred embodiment of the present invention, a cryptographic device includes a de-multiplexer, a plurality of encryption blocks, a plurality of permutation blocks, and a multiplexer. The encryption blocks encrypt data to produce encrypted data. The de-multiplexer receives data portions from a plaintext message and directs the data portions to one of the encryption blocks, based on a value within a path control session key. Each permutation block is associated with an encryption block. Each permutation block permutes encrypted data from the encryption block associated therewith. The multiplexer receives data portions from each of the plurality of permutation blocks to produce an encrypted output data stream.
For example, each data portion directed by the de-multiplexer means is one byte in length. Each encryption block in the plurality of encryption blocks encrypt data eight bytes at a time.
In the preferred embodiment, two separate keys are used. An encryption session key is used to perform encryption. Different portions of the path control session key are used to control the de-multiplexer, the multiplexer and the permutation blocks.
The present invention offers significant additional protection against attacks on secrecy. Brute-force ciphertext-only attacks are greatly hindered. In a simple two encryption block system there are 12,870 different ways that the eight byte block output from one encryption block can appear in a sixteen byte transmission (i.e. combined with the eight byte output from the other encryption block). Since there are 40,320 different ways (i.e. permutations) that these eight bytes can be arranged there are, therefore, approximately 520 million combinations of ciphertext associated with a single block transmission. If an eavesdropper can successfully perform a decryption brute-force ciphertext-only attack in 3.5 hours on a single encryption block, when two encryption blocks are connected in parallel, and permutation is performed on each encryption block, it will take almost 208,000 years to perform the same attack (3.5 hoursxc3x97518,918,400 combinations=207,900 years).
Plaintext attacks on this system also get hindered by embodiments of the present invention. Since there are plaintext attacks (e.g. Differential Cryptanalysis) which can be more efficient than brute-force attacks, the correlation between plaintext and ciphertext is further obscured by adding the de-multiplexing means to the input of the encryption blocks. If an eavesdropper can successfully perform some form of intelligent plaintext encryption attack in 3 to 15 minutes on a single encryption block, when two encryption blocks are connected in parallel, and permutation is performed on each encryption block, it will take approximately 38 million years to perform the same attack (3 minutesxc3x9712870xc3x97518,918,400=38,332,900 years). Clearly, when the present invention is utilized, plaintext attacks become less efficient than brute force ciphertext-only attacks.